1. Field of the Invention
The present invention relates generally to the art of synthetic foams and more particularly to foams used, for example, in refrigeration and other thermal insulation applications. In its most preferred embodiment, the present invention relates to urethane or polyisocyanurate foams of the type previously blown with solvent or CO.sub.2. Still more specifically the present invention relates to such foams prepared under reduced pressure. In its most preferred form, the present invention relates to foams produced under reduced pressure and the encasement of such foams in materials which will prevent ambient air from entering the foam voids, thereby maintaining a reduced pressure within the voids thereby enhancing the K-factor and minimizing the need, in some applications, for the use of blowing agents which are detrimental to the environment.
2. Description of the Prior Art
Many different types of foams are known in the art for use in refrigeration and other applications where thermal insulation is desired. A myriad of other applications also exist for such foams. Foam preparation, in and of itself, is well known to those skilled in the art and the starting materials can vary widely. Polystyrene foams have been used for applications such as drinking cups, food containers, household articles and the like. Urethane and polyisocyanurate foams have been known for many years and are especially effective for applications where it is desired to provide a thermal barrier. Typically applications include building panels, refrigeration insulation, the use of such foams in coolers, drink holders, vacuum bottles, and the like. While the remainder of the application will focus on the use of the present invention in the field of urethane and isocyanurate foams, it should be understood from this point forward that the invention is not to be limited to such foams but may be used with other types of foams, including the polystyrene previously mentioned as well as polyethylene, foaming synthetic rubber foam, etc. Once the principals of the present invention are understood by those skilled in the art, it will be readily appreciated how the improvements of the present invention may be incorporated into other foam preparation systems.
In the case of polyurethane and polyisocyanurate foams, a variety of starting materials are disclosed in the prior art, including the prior art patents discussed below. In a common system, two components are used, one of the components being an organic polyol and the other being an organic polyisocyanate. Halogenated alkane blowing agents may be added to the system to result in what have come to be known as "solvent" blown systems. Typical of such blowing agents are Freon-11.RTM., Freon-12.RTM. and Freon-141b.RTM.. In the manufacture of this type of foam, the reaction of the polyisocyanate and the polyol results in the formation of heat which causes rapid evaporation of the blowing agent and the creation of cell voids while the foam is in a plastic or uncured condition. Other typical starting materials for these types of foams include surfactants and catalysts for the reaction of the polyol and isocyanate radicals of the starting materials.
An alternative to the use of solvents is the use of "water" blown systems, wherein water is added to the polyol component, which in turn reacts with the isocyanate radicals of the polyisocyanate to produce carbon dioxide.
In either of the above cases, and in the case of the preparation of other types of foams in which a blowing agent or gas is created in situ during form formation, the gas in the resin expands as it approaches an equilibrium pressure with the atmosphere. When the foam has risen and the plastic resin has been cured, the cells of the foam will be filled with whatever gas has been used to form them. The conductivity of the resultant foam will then be a summation of the conductivity of the organic resin components of the foam combined with the conductivity of the particular gas which has been involved.
Several difficulties have arisen, especially in recent years, with such foams and especially in the use of blowing agents which include chlorinated solvents. Much attention has been directed toward the elimination of such blowing agents, leaving the industry to develop techniques for maintaining suitable K-factors in foams used for a variety of important commercial applications. Tradeoffs are encountered with current technology, in that reduced K-factors may result in higher electrical costs in application such as refrigeration. Similarly, if the foam was used in building insulation panels, lower K-factors would result in higher heating and cooling requirements for a particular building or thicker layers of the foams, also involving a tradeoff in manufacturing costs and space requirements, would be required.
The following U.S. Patents disclose various foam forming components which would be useful in forming the improved foams of the present invention. They are disclosed here in lieu of detailed descriptions of the mechanisms of foam formation and in lieu of detailed listings of those catalysts, surfactants, polyols and polyisocyanates which have been heretofore used in the art. These patents, which are representations of the art, should be taken as illustrative rather than limiting.
The patents include Carlstrom et al. U.S. Pat. No. 4,223,068 issued Sep. 16, 1980 for "Rigid Polyurethane Foam Containing Polyester Residue Digestion Product and Building Panel Made Therefrom"; U.S. Pat. No. 4,444,919 issued Apr. 24, 1984 to Brennan for "Use of Polyethylene Terephthalate Liquid Waste Streams Containing Glycols as Rigid Polyol Extenders"; U.S. Pat. No. 4,710,521 issued Dec. 1, 1987 to Soukup et al. for "Catalyst Mixtures for Polyisocyanurate Foam"; U.S. Pat. No. 4,604,410 issued Aug. 5, 1986 to Altenberg for "Manufacturing of Rigid Foam Using Etherified Modified Aromatic Polyols"; Grigsby, Jr. et al. U.S. Pat. No. 4,469,824 issued Sep. 4, 1984 for "Liquid Terephthalic Ester Polyols and Polyisocyanurate Foam Therefrom", and U.S. Pat. No. 4,417,001 issued Sep. 22, 1983 to Svoboda et al. for "Low Smoke Isocyanurate Modified Urethane Foam and Method of Making Same." The latter patent is representative of several within the foregoing group which employ waste streams or recovered materials for use in the polyol component of the foam. These particular materials when used in the present invention provide the dual environmental advantage of recovery or recycling, as well as the elimination of harmful blowing agents.
A method for preparing foams, and the foam product prepared by the method, which would result in foams having desirable K-factors and which would eliminate the undesirable blowing agents used in the prior art would represent a significant advance in this art.